Letter | Published:

Sequential faulting explains the asymmetry and extension discrepancy of conjugate margins

Nature volume 468, pages 294299 (11 November 2010) | Download Citation


During early extension, cold continental lithosphere thins and subsides, creating rift basins. If extension continues to final break-up, the split and greatly thinned plates subside deep below sea level to form a conjugate pair of rifted margins. Although basins and margins are ubiquitous structures, the deformation processes leading from moderately extended basins to highly stretched margins are unclear, as studies consistently report that crustal thinning is greater than extension caused by brittle faulting1,2,3,4. This extension discrepancy might arise from differential stretching of brittle and ductile crustal layers2, but that does not readily explain the typical asymmetric structure of conjugate margins5,6—in cross-section, one margin displays gradual thinning accompanied by large faults, and the conjugate margin displays abrupt thinning but smaller-scale faulting5. Whole-crust detachments, active from early in the rifting, could in theory create both thinning and asymmetry1, but are mechanically problematical. Furthermore, the extension discrepancy occurs at both conjugate margins, leading to the apparent contradiction that both seem to be upper plates to a detachment fault7,8. Alternative models propose that much brittle extension is undetected because of seismic imaging limitations caused either by subseismic-resolution faulting9, invisible deformation along top-basement 100-km-scale detachments8 or the structural complexity of cross-cutting arrays of faults3. Here we use depth-migrated seismic images to accurately measure fault extension and compare it with crustal thinning. The observations are used to create a balanced kinematic model of rifting that resolves the extension discrepancy by producing both fault-controlled crustal thinning which progresses from a rift basin to the asymmetric structure, and extreme thinning of conjugate rifted margins. Contrary to current wisdom, the observations support the idea that thinning is to a first degree explained by simple Andersonian faulting that is unambiguously visible in seismic data.

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  1. 1.

    , & Detachment models for the formation of passive continental margins. Tectonics 10, 1038–1064 (1991)

  2. 2.

    & in Proc. NSF Rifted Margins Theor. Inst. (ed. Karner, G. D.) 92–136 (Columbia Univ. Press, 2004)

  3. 3.

    Extension discrepancy at North Atlantic nonvolcanic rifted margins: depth-dependent stretching or unrecognized faulting? Geology 35, 367–370 (2007)

  4. 4.

    New constraints on the formation of the non-volcanic continental Galicia–Flemish Cap conjugate margins. J. Geol. Soc. Lond. 149, 829–840 (1992)

  5. 5.

    et al. Continental break-up and the onset of ultraslow seafloor spreading off Flemish Cap on the Newfoundland rifted margin. Geology 32, 93–96 (2004)

  6. 6.

    & The deep structure of non-volcanic rifted continental margins. Phil. Trans. R. Soc. Lond. A 357, 767–804 (1999)

  7. 7.

    & Lower crustal extension across the Northern Carnarvon basin, Australia: evidence for an eastward dipping detachment. J. Geophys. Res. 103, 4975–4991 (1998)

  8. 8.

    &. Manatschal, G. A mechanism to thin the continental lithosphere at magma-poor margins. Nature 440, 324–328 (2006)

  9. 9.

    & Amount of extension on “small” faults: an example from the Viking graben. Geology 20, 47–50 (1992)

  10. 10.

    , & Evolution of magma-poor continental margins from rifting to seafloor spreading. Nature 413, 150–154 (2001)

  11. 11.

    et al. Contourites in the Galicia Bank region (NW Iberian Atlantic). Mar. Geophys. Res. (in the press)

  12. 12.

    , & Spacing and linkage of confined normal faults: importance of mechanical thickness. J. Geophys. Res. 111, B01402 (2006)

  13. 13.

    , & The geometric and statistical evolution of normal fault systems: an experimental study of the effects of mechanical layer thickness on scaling laws. J. Struct. Geol. 23, 1803–1819 (2001)

  14. 14.

    & Rheological evolution during extension at passive non-volcanic margins: onset of serpentinization and development of detachments leading to continental break-up. J. Geophys. Res. 106, 3961–3975 (2001)

  15. 15.

    et al. The evolution of amphibolites from Site 1067, ODP Leg 173 (Iberia Abyssal Plain): Jurassic rifting to the Pyrenean compression. Spec. Publ. Geol. Soc. (Lond.) 187, 191–208 (2001)

  16. 16.

    , & Cooling history and exhumation of lower-crustal granulite and upper mantle (Malenco, eastern central Alps). J. Petrol. 41, 175–200 (2001)

  17. 17.

    & Drilling on the Galicia Margin: retrospect and prospect. Proc. ODP Sci. Results 103, 809–828 (1988)

  18. 18.

    Wilson, R. C. L., Manatschal, G. & Wise, S. Rifting along non-volcanic passive margins: stratigraphic and seismic evidence from the Mesozoic of the Alps and Western Iberia. Spec. Publ. Geol. Soc. (Lond.) 187, 429–452, 2001.

  19. 19.

    , , & Tectonosedimentary evolution of the deep Iberia-Newfoundland margins: evidence for a complex break-up history. Tectonics 26, TC2011 (2007)

  20. 20.

    , , , & Spatio-temporal evolution of strain accumulation derived from multi-scale observations of Late Jurassic rifting in the northern North Sea: a critical test of models for lithospheric extension. Earth Planet. Sci. Lett. 234, 401–419 (2005)

  21. 21.

    et al. Strain localisation and population changes during fault system growth within the Inner Moray Firth, northern North Sea. J. Struct. Geol. 25, 307–315 (2003)

  22. 22.

    et al. Normal fault growth, displacement localisation and the evolution of normal fault populations: the Hamman Faraun fault block, Suez Rift, Egypt. J. Struct. Geol. 25, 1347–1348 (2003)

  23. 23.

    et al. Tectonic evolution of fault-bounded continental blocks: comparison of paleomagnetic and GPS data in the Corinth and Megara basins (Greece). J. Geophys. Res. 109, B02106 (2004)

  24. 24.

    & Styles of extensional decoupling. Geology 26, 699–702 (1998)

  25. 25.

    & Symmetric and asymmetric lithospheric extension: Relative effects of frictional-plastic and viscous strain softening. J. Geophys. Res. 108, 2496 (2003)

  26. 26.

    Fluid involvement in normal faulting. J. Geodyn. 29, 469–499 (2000)

  27. 27.

    et al. Movement along a low-angle normal fault: the S reflector west of Spain. Geochem. Geophys. Geosyst. 8, Q06002 (2007)

  28. 28.

    New models for evolution of magma-poor rifted margins based on a review of data and concepts from West Iberia and the Alps. Int. J. Earth Sci. 93, 432–466 (2004)

  29. 29.

    , , , & Magnetic evidence for slow spreading during the formation of the Newfoundland and Iberian margins. Earth Planet. Sci. Lett. 182, 61–76 (2000)

  30. 30.

    et al. The ocean-continent boundary off the western continental margin of Iberia: crustal structure west of Galicia Bank. J. Geophys. Res. 101, 28291–28314 (1996)

  31. 31.

    The dynamics of faulting. Trans. Edinb. Geol. Soc. 8, 387–402 (1905)

  32. 32.

    Seeking Anderson’s faulting in seismicity: a centennial celebration. Rev. Geophys. 46, RG4001 (2008)

  33. 33.

    & A simple model for the fault-generated morphology of slow-spreading mid-ocean ridges. J. Geophys. Res. 100, 561–570 (1995)

  34. 34.

    Active normal faulting and crustal extension. Spec. Publ. Geol. Soc (Lond.) 28, 3–17 (1987)

  35. 35.

    & Fault and bed ‘rotation’ during continental extension: block rotation or vertical shear? J. Struct. Geol. 15, 753–770 (1993)

  36. 36.

    Marsden, G. & Egan, S. S. A flexural-cantilever simple-shear/pure-shear model of continental lithosphere extension: applications to the Jeanne d’Arc Basin, Grand Banks and Viking Graben, North Sea. Spec. Publ. Geological Society (Lond.) 56, 41–60 (1991)

  37. 37.

    et al. Extreme crustal thinning in the south Porcupine Basin and the nature of the Porcupine Median High: implications for the formation of non-volcanic rifted margins. J. Geol. Soc. Lond. 161, 783–798 (2004)

  38. 38.

    , , & Conjugate margins of Canada and Europe: results from deep reflection profiling. Geology 17, 173–176 (1989)

  39. 39.

    , , & Evolution of nonvolcanic rifted margins: new results from the conjugate margins of the Labrador Sea. Geology 23, 589–592 (1995)

  40. 40.

    , , & Mechanisms of extension at nonvolcanic margins: evidence from the Galicia interior basin, west of Iberia. J. Geophys. Res. 108, 2245 (2003)

  41. 41.

    , , , & Imaging a lithospheric detachment at the continent–ocean crustal transition off Morocco. Earth Planet. Sci. Lett. 241, 686–698 (2006)

  42. 42.

    , , & Segmentation and along-strike asymmetry of the passive margin in Socotra, eastern Gulf of Aden: are they controlled by detachment faults? Geochem. Geophys. Geosyst. 8, Q03007 (2007)

  43. 43.

    & Plate motions and continental extension at the rifting to spreading transition in Woodlark Basin, Papua New Guinea: can oceanic plate kinematics be extended into continental rifts? Tectonophysics 458, 82–95 (2008)

  44. 44.

    Flexural rotation of normal faults. Tectonics 7, 959–973 (1988)

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The ideas presented in this work have benefited from discussions with J. Adam, A. Amilibia, E. Casciello, T. Cunha, M. R. Fowler, S. Hardy, J. García-Pintado, G. Manatschal, K. McClay, M. Menzies, E. Saura and F. Storti, and from numerous discussions and previous collaborations with T. J. Reston. The early work that led to the ideas presented here was carried out when C.R.R. worked at IFM-GEOMAR and M.P.-G. at IFM-GEOMAR and later at ICTJA-CSIC. We are grateful to J. Collier and C. Beaumont for their reviews, which helped improved this article. This is a publication of the Department of Earth Sciences of the Royal Holloway, University of London. C.R.R. has been supported by the Kaleidoscope project, funded by Repsol, and by the Spanish National Project Medoc of the Ministry of Science and Innovation.

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Author notes

    • César R. Ranero
    •  & Marta Pérez-Gussinyé

    These authors contributed equally to this work.


  1. ICREA at CSIC, Barcelona Center for Subsurface Imaging, Instituto de Ciencias del Mar, CSIC, Passeig Marítim de la Barcelona 37-49, 08003, Barcelona, Spain

    • César R. Ranero
  2. Department of Earth Sciences, Royal Holloway, University of London, Egham TW20 0BD, UK

    • Marta Pérez-Gussinyé


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C.R.R. processed the seismic data up to pre-stack depth migration and interpreted them. M.P.-G. built the tectonic model. Both authors contributed equally to writing the manuscript and to developing the ideas behind the tectonic model.

Competing interests

The authors declare no competing financial interests.

Corresponding authors

Correspondence to César R. Ranero or Marta Pérez-Gussinyé.

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